Find the Nearest Color with C# - Using the Euclidean Distance between Two Colors

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Description

This small method provides an algorithm to find the nearest (or "most similar") color in a given "colorspace" compared to a given single color. This is done by searching for the least Euclidean distance between the two colors. The Euclidean distance can be computed in an arbitrary n-dimensional space. In this implementation, the value for the alpha-component of the given color to "approximate" is NOT used. In the sample, I have used a little bit of code written by Julijan Sribar (http://www.codeproject.com/cs/miscctrl/MultiTabColorPicker.asp) to receive the "web colors" as the sample color space. The webcolor-space is actually a subspace of the RGB-space.

The Algorithm

It is quite simple to compute the Euclidean distance between two points. First, convert the three color-components to double-values:

double dbl_input_red = Convert.ToDouble(input_color.R);
double dbl_input_green = Convert.ToDouble(input_color.G);
double dbl_input_blue = Convert.ToDouble(input_color.B);

Further define a "similarity measure" (actually this is THE distance). This measure has to be initialized by an arbitrary value which must be greater than the greatest possible distance (basically this is the distance between white and black).

double distance = 500.0;

The algorithm to find the least distance is quite simple:

Color nearest_color = Color.Empty;
foreach (object o in WebColors)
{
	// compute the Euclidean distance between the two colors
	// note, that the alpha-component is not used in this example
	dbl_test_red = Math.Pow(Convert.ToDouble(((Color)o).R) - dbl_input_red, 2.0);
	dbl_test_green = Math.Pow(Convert.ToDouble
		(((Color)o).G) - dbl_input_green, 2.0);
	dbl_test_blue = Math.Pow(Convert.ToDouble
		(((Color)o).B) - dbl_input_blue, 2.0);
	// it is not necessary to compute the square root
	// it should be sufficient to use:
	// temp = dbl_test_blue + dbl_test_green + dbl_test_red;
	// if you plan to do so, the distance should be initialized by 250000.0
	temp = Math.Sqrt(dbl_test_blue + dbl_test_green + dbl_test_red);
	// explore the result and store the nearest color
	if(temp == 0.0)
	{
		// the lowest possible distance is - of course - zero
		// so I can break the loop (thanks to Willie Deutschmann)
		// here I could return the input_color itself
		// but in this example I am using a list with named colors
		// and I want to return the Name-property too
		nearest_color = (Color)o;
		break;
	}
	else if (temp < distance)
	{
		distance = temp;
		nearest_color = (Color)o;
	}
}

Use

To use the code, simply copy and paste the method GetNearestWebColor(Color input_color) into your project. Alternatively you can place a reference to SampleLibrary.dll.

History

• 6^th January, 2007: Initial post

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)